Mods for cheap FM dual band rig: Baofeng UV-3R

I’ve bought for less of 40eu this little handeld rtx.

It works quite well but needs some mods.

On 70cm all is ok, on 145 MHz the second harmonic is only 20dB down to the carrier…

This is due to large design of output Low Pass Filter to cover the whole band 136-174 MHz, but in my country we can only transmit on FM between 144.5 – 145.8 and the 2nd harmonic on 290MHz can’t be well filtered.

I’ve found on Yahoo Group of UV-3R a simple mod for drop down the second harmonic by adding a single 47pF capacitor.

Another useful mod is decrease the BF audio level, too high by default also at the lowest volume step.

LPF:

Spectrum before the mod on 145 and 431 MHz (click to enlarge)

Spectrum after the mod on 145 and 431 MHz

As we can see the 2nd harmonic on 145MHz is lowered by about 20dB, reaching the more convenient level of 40dBc, on 70cm no significant change.

Power measured on 145 and 430 MHz

VOLUME MOD

The volume reduction is obtained simply by placing a resistor of 56k above (in parallel) the existing 100k as feedback for audio power amp

Sorry I made a mistake. I am a paraglider I use this radio in the air on 144.775 Although I use SQL on 9 my radio gets some loud noise and shout in every 2-7sec for 0.5 – 3 sec. It is very annoying. I thought my GPS’s processor makes some noise, but yesturday I flied without GPS and mobile phone but the phenomenon has not disappeared. :( Your modification could help me?

I have compared it with a non modified Baofeng and this last has better modulation. The problem is that I didn’t check the audio before making the mod and now I don’t know if it was done by me or if it’s a factory problem.

The audio mod doesn’t make any change in my case – I soldered 56k resistor in paralell. I am sure I did it properly. What the heck is going on?
BTW, can I see properly that you get almost 5W output from UV-3R? 73s

All transmitters transmit on their frequency and with less power on multiples. A good rule is to minimize the power output at frequencies other than the fundamental, where we are not allowed to transmit. In this case only only one capacitor is required to fix the filter, why not do it?

I didn’t find it to be harmful with so low output, but the question was – should I do it asap due to any more serious reason, here where I live I gotta make some more effort to get the capacitor.
BTW after using Baos a little, the only term which can excouse so many bugs and lacks is the price. Won’t change my vx-7 anyway, but the price will allow me to keep the second lightweight ht for less serious and rare PMR use with non-hams (yeah, I know, I know about PMR).

With this spectrum the rig probably isn’t compliant with the european R&TTE rules, I remember >35dBc or so. On the other hand no one will ever know and your rig will works fine with a minimal power wasted.
GL with your callsign, see you on air
73